A locator system for use in a conventional car navigation system typically carries out a dead reckoning process of determining the traveling direction of a vehicle using a gyro sensor, also determining the traveled distance of the vehicle using a speed sensor, and using the results of the determinations. In this dead reckoning, a point which is used as a reference is measured first with GPS (Global Positioning System) or the like, the traveling direction and traveled distance of the vehicle from the point are determined to calculate a movement vector, and this movement vector is added to the reference position to acquire the current position of the vehicle. The traveling path of the vehicle can be determined by repeating this process while the vehicle being navigated is traveling.
In order to prevent an error occurring in the estimated position resulting from an error of the measurement by the gyro sensor and an error of the measurement by the speed sensor from being accumulated, a position error in the result of positioning using GPS is corrected at an arbitrary time. However, an error of about 10 m may occur also in the positioning using GPS, and the position coordinates of the vehicle may not be acquired correctly even if the vehicle position is corrected using the result of the positioning using GPS during the dead reckoning.
Furthermore, a gyro sensor mounted in currently-used car navigation systems does not have angle detection accuracy that is good enough to support all states which can occur while the vehicle is traveling, and therefore the detection result of the gyro sensor cannot easily draw a distinction between a straight ahead movement and a turn movement when the vehicle changes its heading at a narrow angle with respect to a branch point and when the vehicle makes a lane change. Therefore, it is difficult for conventional car navigation systems to determine promptly and correctly in which direction the vehicle has been headed after passing a branch point.
In contrast with this, a traveling route estimating device disclosed by, for example, patent reference 1 takes into consideration the fact that, when the vehicle is making a turn when passing through an intersection (when the vehicle is making a right- or left-hand turn), it becomes impossible to correctly specify the direction in which the vehicle is traveling because of the turn, and, when the vehicle makes a turn after having moved forwardly over a predetermined distance at which the traveling route estimating device determines whether the vehicle makes a direction change after entering the intersection, does not estimate the traveling route, whereas when the vehicles does not make a turn after having moved forwardly over the predetermined distance, the traveling route estimating device determines that the vehicle has moved straight through the intersection and then estimates the traveling route. By doing in this way, even if the traveling route estimating device prohibits the estimation of the traveling route at the time when the vehicle passes through an intersection in order not to use the traveling route in which an error occurs when the vehicle changes its direction at the branch point, the traveling route estimating device can return to the vehicle control based on the information about the traveling route at an earlier time after the vehicle has passed through the intersection.